Differences between populations and tissues of Litopenaeus vannamei infected with Enterocytozoon hepatopenaei

Abstract:

Growth-related parameters of individuals from four populations of Litopenaeus vannamei from Huanghua of Heibei Province (HH), Pingdu of Shandong Province (PD), Wujiang of Jiangsu Province (WJ), and Rizhao of Shandong Province (RZ) were assessed. Amount of Enterocytozoon hepatopenaei (EHP) in the hepatopancreas of individuals from all populations and EHP in multiple tissues of shrimp from the RZ population were assessed with TaqMan-based quantitative PCR. The results showed that the RZ population possessed optimal growth-related parameters and the lowest EHP among the four populations. The histograms of case-logarithmic EHPs of the four populations presented different modes. The case distribution of logarithmic EHPs from the HH and PD populations showed double peaks, while those of the WJ and RZ populations showed a single peak. The different distribution modes may indicate a different EHP spread in the four populations. The population with a single peak mode or the higher logarithmic EHP subpopulation isolated from the population with a multiple peak mode showed a significant negative correlation with shrimp body length or body weight to logarithmic EHP. The EHP detected in different tissues of the RZ population followed the order (from highest to lowest), EHP in hepatopancreas > EHP in midgut > EHP in hemolymph > EHP in gills > EHP in muscle. The logarithmic EHP in the hepatopancreas–midgut, hepatopancreas–gills, and midgut–gills had a significant correlation level above 99.9% (P<0.001), while the logarithmic EHP of the other two tissues had a significant correlation level above 99.0% (P<0.01) or above 99.5% (P<0.05), except for midgut–hemolymph and hepatopancreas–hemolymph. In-situ hybridization of a DIG-labeled EHP probe in the hepatopancreas, muscle, gills, and midgut showed that the hepatopancreas is the major target tissue of EHP infection in shrimp. Minor and weak hybridization signals were also observed in other tissues, which indicated that a few cells in those tissues were also susceptible to EHP infection in L. vannamei.